An eccentric oscillation-type gear device disclosed in Patent Document 1 includes: a crank shaft having an eccentric part; an oscillation gear having an insertion hole to which the eccentric part of the crank shaft is inserted, and a tooth part; an external cylinder having an internal tooth to be meshed with the tooth part of the oscillation gear; and a carrier disposed inside the external cylinder and hold the oscillation gear through the crank shaft. In the gear device, a closed space for accommodating the oscillation gear is defined by the external cylinder and the carrier. The carrier is provided with a plurality of through-holes which communicate the closed space with the outside. An oil seal cap is fitted in each of the through-holes. These oil seal caps are provided to confine lubricating oil enclosed in the aforementioned closed space.
An oil seal cap (oil sealing member), which has a discoid bottom plate and an annular cylindrical part projecting from an outer circumferential part of the bottom plate, is fitted in a through-hole of the plurality of through-holes, which is formed to opposedly to a radial center of the oscillation gear. In addition, an oil seal cap, which has a body part having an oil hole passing therethrough, and a plug member that closes the oil hole, the plug member being removable from the body part, is fitted in a through-hole of the plurality of through-holes, which is formed for attaching thereto the crank shaft.
According to the latter oil seal cap, during changing of the lubricating oil enclosed in the closed space, the lubricating oil changing operation can be carried out by removing only the plug member without removing the body part. Thus, the lubricating oil changing operation can be efficiently carried out.